Oligotrophic and eutrophic MICP treatment for silica and carbonate sands

Abstract

The terms ‘oligotrophic treatment’ and ‘eutrophic treatment’ have been introduced to differentiate between whether fixation liquid or nutrients have been administered during the on-site process for microbially induced precipitation of calcite. Results from scanning electron microscopy images for small-scale soil column tests have shown the different treatments to have markedly different precipitation patterns, crystal morphology and bond formation and eventual bond failure in silica sand. In the case of oligotrophic treatment, the fixation phase led to a more widespread pattern of precipitation in silica sand particles, which resulted in large single rhombohedral crystals being formed on the surface of particles or at particle contact points when nutrients were withheld on site. In contrast, eutrophic treatment involving the on-site delivery of nutrients promoted preferential precipitation at particle contact points in the form of micritic dome-like structures of vaterite that acquired a new layer of crystal with each delivery of nutrients. The different crystal morphologies were found to influence particle-bond failure mechanism in the form of either a particle-bond interface mode of failure or an internal failure of the carbonate crystal along a suture.